Proposal Summary Heart failure with preserved ejection fraction (HFpEF) accounts for ?50% of all patients with heart failure, and is associated with significant morbidity, mortality and health care expenses. Yet no effective treatment for HFpEF has been identified. Commonly coexisting with other metabolic diseases, HFpEF is considered as the cardiovascular manifestation of a systemic metabolic disturbance. However, little is known about its underlying mechanisms. Our laboratory recently developed and validated a novel mouse model that faithfully recapitulates most clinical features of human HFpEF. Using this model, we discovered significant myocardial mitochondrial morphology changes indicating possible dysfunction, a potential common pathway linking metabolic distress with cardiac dysfunction. Therefore, the current proposal aims to identify specific mitochondrial defects and metabolic changes in HFpEF myocardium and their underlying mechanisms. Our preliminary data suggest that HFpEF mitochondria harbor a specific defect in fatty acid oxidation (FAO), which is accompanied by significant mitochondrial protein hyperacetylation. Further study is proposed to test whether hyperacetylation of key FAO enzymes, a known mechanism that impairs FAO in other metabolic diseases, also play a role in HFpEF. Given the fact that protein acetylation is a reversible process, we will test both in vitro and in vivo whether pharmacological agents that reverse protein hyperacetylaition attenuate mitochondrial dysfunction and improve cardiac function. Collectively, these studies will provide important insights into the mitochondrial metabolic defects characteristic of HFpEF. By focusing on reversible protein acetylation, the findings will have potential for immediate clinical translation. Furthermore, this work will serve as a critical platform for future mechanistic studies of HFpEF pathogenesis and for the next stages of my training.